1. Field of the Invention
The present invention is related to load management and control for power utilities and, more particularly, is directed to a method and apparatus for permitting an electric utility to selectively control distribution of its power to a plurality of customer loads.
2. Description of the Prior Art
Most electrical power utilities in the United States must construct their power generating plants with sufficient capacity to meet the total customer power demand at any given point in time. This means that although maximum or peak power demands may occur only relatively infrequently, when compared with the average power demand, the utility must nevertheless have the power generating capacity to meet the peak demand. Many utilities therefore either pay for or charge their customers in accordance with peak power demands rather than average or actual power consumed. If the peak power demand periods can therefore be minimized or controlled, savings to the customer and utility will be effected.
The foregoing situation has led to the development of load management systems for use by electric power utilities which permit them to control peak demands on the power generating equipment by turning off and on various customer loads during various times. Various types of customer loads which can be regulated in this manner to control and minimize peak power demand include, for example, electric hot water heaters, air conditioning compressors, electric space heaters, and the like.
One type of load management control technique is known as the ripple tone injection method. In such a system, audio frequency pulses are coded by control function and are impressed directly onto the utility's power lines. Receivers located at the customer loads respond to the coded pulses to effect the desired command function.
It is known to provide electromechanical ripple control transmitters, consisting of a motor/alternator set operating through thyristor static switches, to apply the pulse coding to the power lines. It has also recently been proposed to utilize static frequency converters, consisting of a static inverter and suitable coupling network, for a ripple control transmitter. See, for example, "Pulse Coded Inverter For Utility Load Management System", Galloway and Berman, IAS 1977 Annual, pages 149 through 155.
Known U.S. patents which relate to power load management include: U.S. Pat. Nos. 3,359,551; 3,886,332; 3,972,470; 4,064,485; 4,075,699; and 4,130,874.
In U.S. Pat. No. 3,359,551, for example, a system is disclosed for controlling the operation of a power distribution network in which signals are transmitted over power lines to a plurality of receivers which perform electrical circuit connections and disconnections in response to the received signals. In this system, the signals contain address and command information so that one of a plurality of receivers are selected in response to the address portion and a predetermined function is performed in response to the command portion. The transmitter at a selected location employs derivatives of these signals to produce predetermined sequences of relatively high frequency carrier bursts to be fed to the power lines for distribution to tuned receivers at the other end of the line.
In U.S. Pat. No. 4,075,699, a power monitoring and load shedding system is described which includes power consumption metering for entering overall power consumption into a central processing unit. Circuitry is provided for the central processing unit to turn local and remote loads on and off in accordance with stored energy consumption projecting and load shedding algorithms.
While each of the prior art systems appear useful in a given context, a practical, centralized load management control system for electric utilities must be cost effective in order that the savings resulting from load management outweighs the cost to the utility and the consumer of the load management system. It is toward achieving this broad objective that the present invention is advanced.